M. Moldes et al., H-1-H-2 EXCHANGE IN THE PERFUSED-RAT-LIVER METABOLIZING [3-C-13]ALANINE AND (H2O)-H-2 AS DETECTED BY MULTINUCLEAR NMR-SPECTROSCOPY, NMR in biomedicine, 7(6), 1994, pp. 249-262
Citations number
50
Categorie Soggetti
Spectroscopy,"Radiology,Nuclear Medicine & Medical Imaging",Biophysics,"Medical Laboratory Technology
The exchange of individual protons of hepatic metabolites against the
solvent deuterons has been investigated in perfused rat liver. Livers
from starved rats were perfused for 20 min with a 10 mM solution of un
labeled or 3-C-13-labeled L-alanine in Krebs Ringer bicarbonate buffer
, with or without 50% deuterium oxide ((H2O)-H-2). High resolution C-1
3 NMR analysis of deuterium-induced isotopic shifts and of H-2-C-13 co
uplings revealed a differential H-1-H-2 exchange depending on the chem
ical nature of the metabolite and on the site of C-13 labeling. [3-C-1
3]Aspartate isotopomers showed similar H-2/H-1 ratios in the C3 and in
the C2 carbons while [2-C-13]aspartate isotopomers had much smaller H
-2/H-1 ratios in the C2 than in the C3 carbons. Similarly, [2-C-13]glu
tamate isotopomers had H-2/H-1 ratios significantly smaller in the C2
than in the C3 carbon. These results suggest that the hydration-dehydr
ation reactions of the citric acid cycle, which result in exchange at
the C3 carbons of aspartate and glutamate, approach equilibrium with t
he perfusate faster than the aminotransferases of aspartate and alanin
e, which induce exchange at the C2 carbons of these amino acids. Taken
together, the results obtained are consistent with a heterogeneous so
lvent exchange environment in the perfused liver.